Isomerization of 1-olefins or transolefins to internal cis-olefins

ABSTRACT

THE ISOMERIZATION OF 1-OLEFINS OR TRANS-OLEFINS TO INTERNAL CIS-OLEFINS IS ACCOMPLISHED BY MEANS OF A CATALYST SYSTEM COMPRISING AN ORGANOLITHIUM COMPOUND WITH A POTASSIUM SALT OF A FATTY ACID OR OF AN ALOCOHOL. FOR EXAMPLE, 1-BUTENE YIELDS CIS-2-BUTENE.

fl lnited States Patent fice' 3,792,109 Patented Feb. 12, 1974 ABSTRACT OF THE DISCLOSURE The isomerization of l-olefins or trans-olefins to internal cis-olefins is accomplished by means of a catalyst system comprising an organolithium compound with a potassium salt of a fatty acid or of an alcohol. For example, l-butene yields cis-Z-butene.

The invention relates to a process for converting l-olefins to internal cis-olefins. In another aspect, the invention relates to a method of converting trans-olefins containing an internal double bond to the cis-isomer. In another aspect, the invention relates to a method of increasing the proportion of cis-isomer in cis/ trans mixtures.

BACKGROUND OF THE INVENTION Cis-isomers, relative to the corresponding trans configuration, are less available, more expensive to obtain, less stable, but more reactive. A cis configuration, being relatively energyrich, is convertible under thermal or catalytic influence to the lower energy state, i.e., trans form, with the driving force for the conversion being the difference in energy content between the two isomers. Characteristically, cis-isomers exhibit higher octane numbers than corresponding trans-isomers. The cis-isomers in suitable carbon atom range are more desired for motor fuel purposes, or for certain rubber synthesis requirements such as in EPR rubber synthesis.

Ordinarily, isomerization of a l-olefin yields an internal olefin of trans or predominantly trans configuration, rather than cis, because the trans configuration is the more stable or lower energy form. Internal olefins, i.e., olefins having an internal double bond, generally reflect a mixture predominately trans in configuration.

Generating a cis-isomer in preference to a corresponding trans-isomer is contrary to the usual thermodynamically favored process. For example, one known means of climbing the thermodynamic Appalachian trail is by the absorption of energy from such as ultraviolet irradiation, which can be employed with some compounds, but is not appropriate for the olefins because of their characteristically low ultraviolet absorbance.

Methods to convert cis/trans mixtures to a higher cis content, or to convert l-olefins to corresponding internal double bond compounds predominantly of the cis configuration, certainly would be desirable.

OBJECTS OF THE INVENTION It is an object of the invention to provide a method of producing cis-olefins. A further object of the invention is to convert trans-olefins to cis configuration.

Other aspects, objects, and advantages of the present invention will become apparent from a study of the disclosure and the appended claims.

BRIEF SUMMARY OF THE INVENTION According to the method of our invention, l-olefins and internal trans-olefins are isomerized in the presence of an organoalkali metal compound-potassium alkoxide or organoalkali metal compound-potassium salt of a fatty acid catalyst system to yield olefin mixtures high in the cis-isomer configuration.

DETAILED DESCRIPTION OF THE INVENTION The process of our invention can be applied to terminal olefins, i.e., 1-olefins, to yield internal olefins of preferentially cis structure, e.g., l-butene yields cis-2-butene preferentially. The process can be applied to internal olefins so as to convert at least a portion of the trans configuration to cis configuration by isomerization. A cis/ trans mixture can be enriched in cis content, such as a 4/5 cis/trans Z-butene mixture can be converted to a 6/4 cis/ trans mixture.

OLEFINS Olefins suitable for our reaction are any of the linear or branched olefins which by our process can be increased as to the cis isomer content. These linear or branched olefins can contain cycloalkyl groups. Presently preferred are those l-olefins or internal olefins containing 4 to 20 carbon atoms per molecule, since these are more readily available. On a commercial basis, those olefins of 4 to 12 carbon atoms presently are of more commercial interest in the integrated oil refining-chemical processing plant more and more frequently termed a petrocomplexity.

Examples of suitable olefins include l-butene, Z-butene, l-octene, 3-nonene, 3-methyl-4-ethyl-6-octene, 2,4,6,8- tetramethyl-7-dodecene, 1-cyclohexyl-3-tetradecene, either as the trans form, or as cis/trans mixtures, and the like. Of course, some l-olefins are not subject to double bond isomerization, such as 3,3-dimethyl-l-butene, as well as some internal olefins cannot undergo double bond isomerization, such as 2,2,5,5-tetramethyl-3-hexene. Thus, our olefins can be defined as those linear or branched olefins which can undergo double bond isomerization. The term olefin is used generically and is not limited to monoolefins, since it is apparent that longer chain diolefins in which the double bonds are fairly far apart also could undergo the double bond isomerization according to our invention.

CATALYST SYSTEM We have discovered a unique catalyst combination that enables us to make the conversion of trans to cis configuration effectively and readily. Neither catalyst entity alone is effective. The catalyst system which we employ in the process of our invention represents an admixture of (I) an organoalkali metal compound and (II) a potassium alkoxide or a potassium salt of a fatty acid.

organoalkali metal compounds can be represented by RM in which M is an alkali metal and is lithium, sodium, potassium, rubidium, or cesium. Presently preferred of these is lithium. In the formula, R represents a hydrocarbon radical which can be alkyl including cycloalkyl, and x an integer of 1 to 4, with R having a valence equal to x. Presently preferred are those RM compounds containing up to 20 carbon atoms, although this is more a matter of convenience rather than a limitation of operability with regard to higher molecular weight species. R also can be an aromatic group, including fused ring aromatic groups, containing 6 to 16 carbon atoms. Alkylated fused rings may not be suitable in some instances in view of the propensity of benzylic hydrogen atoms toward metallation.

Examples of organoalkali metal compounds include methyllithium, isopropyllithium, n-butyllithium, tert-octyllithium, n-decyllithium, cyclohexyllithium, 4-butylcyclohexyllithium, 4 cyclohexylbutyllithium, dilithiomethane, 1,10-dilithiodecane, 1,20 dilithioeicosane, 1,4 dilithiocyclohexane, 1,3,5 trilithiopentane, 1,3,5 trilithiocyclohexane, 1,3,5,8 tetralithiodecane, 1,5,10,20 tetralithioeicosane, 1,2,4,6-tetralithiocyc1ohexane, 1,4 dilithiobenene, l-lithionaphthalene, 9,10-dilithioanthracene, l-lithiochrysene and similar compounds in which other alkali metals mentioned are represented. Less preferred are such as dilithiobutadiene, dilithioisoprene and the like which contain points of unsaturation.

Potassium alkoxides include potassium salts of monohydric, dihydric, and polyhydric alcohols. These can be represented by (KO) R in which R' represents a hydrocarbon radical, preferably secondary or tertiary, and preferably aliphatic, the carbon atom number of which radical strenuous separations applied to the converted solvent diluted product may be undesirable. Where a solvent is employed, the percentage concentration of catalyst plus olefin in the solution can range from 1 to 100. Presently preferred is a range of up to 10 percent such as 2 to 10 is not particularly limited except by convenience, and y percent.

is an integer of l to 3. Presently preferred are R groups Reaction temperatures can be substantially atmospheric containing 3 to 12 carbon atoms, alkyl including cyclotemperature, though the invention is operable at any conalkyl, or mixed types such as cycloalkylalkyl, aralkyl, and venient Operating temperature. Suggested ranges are about the like. Primary potassium alkoxides can also be used Oto 70 C., with the presently preferred range being about with suitable pairing of R and solvent to overcome the 15 to 35 C. The reaction is carried out in the presence relatively low solubility of such (KO) R' compounds. of an inert atmosphere using nitrogen, helium, argon, or

Exemplary compounds include potassium isopropoxide, nonreactive, gaseous hydrocarbons suchas methane or potassium sec-butoxide, potassium tert-butoxide, potasethane, or the like. The reaction can be carried out at any sium tert-pentyloxide or potassium tert-amyloxide, potas- 15 suitable pressure sufiicient to maintain substantially liquid sium eyclohexyloxide, potassium 4-ethylcyclohexyloxide, operation including superatmospheric pressures, although potassium S-cyclohexylhexyloxide, and potassium salts of atmospheric pressure is suitable and convenient. glycerol, glycol, 1,6-hexanediol, and other polyhydric alco- EXAMPLES hols, and the like.

potassium salts of fatty id l can b 1 Particular species employed, whether of olefin or of cata- These can be any of the available monobasic organic acids y components, Particular ratios, amounts, COIIdifiOIlS, of this class These can be represented by KOOCR" in are intended to be illustrative and not limitative Ofthe which R" represents an alkyl radical of 8-22, preferably reasonable and P p scope of our invention- 12-22 carbon atoms, for example potassium laurate, potas- Example I sium stearate and potassium docosanoate.

The ratio f (I) organoalkali metal compound to (H) Equimolar amounts of n-butyll thium in n-heptane solupotassium alkoxide or to potassium salt of fatty acid can h and potasslhm tert'perltyloxlde 1T1 y range widely so long as at least each is present in an tron were combined at about 25 to 28 C. under inert amount elfective for the conversion desired. The particular hltrogeh atmosphere- Olefin to lsomeriled Was introratio may vary depending on the particular l fi 30 duced in an amount equimolar to either metal compound, peratures employed, operating conditions, and the like, and employlhg 5 cyclhhfixahe as Solvent P millimole of whether a solvent is employed. We suggest a range of about olefin and, when deslrhd, a paralfhh hydrocarbon Such as 0.111 to 10:1 mole ratio of alkali metalzpotassium, preszfmFthylpropahe to Serve as an lrlremal Standard for g ently prefer a ratio of 0.9:1 to 1.1:1, and most preferred hquld chromatography The adrhlxthre w agitated at presentis a mole ratio of about 1.5 hours at 25 to 22% u C., and the reaction mixture then The amount of catalyst employed is the amount suitable qufihched y h addrhon of ethanol T116 p i i n f for the degree of conversion desired under the operating the Product rmxmre Was determined y gas-liquid chr0- conditions chosen. A mole ratio of total catalystzolefin p ycan vary considerably since an excess of catalyst does not Compositions of feedstocks and of end products for appear to act unfavorably, and relatively low amounts of various runs are shown in Table I:

TABLE I Feedstock (mmoles) Product isomerized (mmoles) transcistranscis- Run number Butane-1 Butene-Z Butene-Z Butane-1 Butane-2 Butane-2 catalyst may simply require longer contact or reaction The above runs clearly illustrate the effective convertimes, or possibly recycle. However, we presently believe a sion of a l-olefin to the corresponding cis isomer, and the mole ratio range of about 10:1 to 0.121 catalystzolefin to enrichment of the cis content of a cis/trans mixture, acbe satisfactory for most purposes, and presently prefer a cording to the process of our invention. range of about 4:1 to 0.5: 1.

The olefin to be isomerized according to the process of Example 11 our invention, in order to convert it to or enrich the cis content thereof, itself can act as reaction solvent with the i ggg ,fggj g gf gi igga l gn hidii ih ie i e need of added solvent or diluent. However, where desired, activity of either cat a1 yst component alone, as well as the an added solvent or diluent can be employed such as combined catalyst com onents Results obt d h cyclohexane, methylcyclohexane, benzene, isooctane, n- 6 in TableH, p ame ares own heptane, and the like, and other saturated suitable ali- 0 phatics, and the like. Alkylated aromatics presently should TABLE H be avoided because of possible reactivity toward the cata- Mole percent efiiuent lyst system. Of course, mixed solvents or diluents can be employed. Solvents can be used to transport the reactants Run BuLi,- nn-B transf i including the olefin or catalyst system or both to the renumber 1111110165 KTP hutene-l term-1 u a 2 action zone, depending upon type of reactor employed, and 1 0 1 0 0 whether or not any additional solvent or diluent is emi 0 0 ployed for the isomerization reaction itself. 0

On the basis of total weight of catalyst-plus-olefin presg gent versus total weight of solvent or solvents to be em- 2- ployed, there appears to be no particular limit as to the g i g -9 amount of solvent used. Large quantities of solvent mean 1 1 1 $3 1 large quantities of unreacted material to handle and ulti- Butymthium mately separate. Of course, due to the general reactivity of the cis configuration olefin as opposed to the trans form,

b Potassium tert-pentyloxide. 52.9% trans and 47.1% cis in starting mixture.

The above runs clearly show that it is the combined catalyst according to our invention that produces the cis product. Either catalyst system component alone had essentially no effect.

EXAMPLE III Further tests were made employing the general procedure and conditions of Example I, employing pentenes in order to observe conversion thereof according to the process of our invention. Results are shown in Table III.

TABLE III Eflfluent products, mole percent Run BuLi/KTP, transcis- (Dis/trans number Olefin mmoles Pentene-l Pentene-2 Pentene-2 ratio 9 Pentene-l--. 0/0 100 0 0 do 1/1 90. 3 2. 2 7. 5 3. 4/1 11 Pentene-2- 0/0 0 72. 5 27. 4 0. 4/1 12. do l/l 8. 1 50. 2 41. 7 0.8/1

Example 1V Improving the cis proportion in olefin admixtures for purposes such as fuel components is desirable as shown by data in Table IV.

TAB LE IV R Octane number Research Motor 4-methy1-eis-2-pentene 99. 7 84. 5 4-methyl-trans-2-pentene..... 98.0 82. 6 3-methyl-cis-2-hexene 92. 4 80. 0 3-methyl-trans-2-hexene 91. 5 97. 6

B Data from Reference Data for Hydrocarbons and Petro-Suliur Compounds, Phillips Petroleum Company, Special Products Division, Bulletin No. 621, Copyright 1962, revised 1969.

The cis-isomers, thusly, can provide higher octane fuels than the corresponding trans isomers.

Other modifications and alterations of this invention will become apparent to those skilled in the art from the foregoing discussion and examples and it should be understood that this invention is not to be unduly limited thereto.

We claim:

1. A method of converting an olefin to a cis configuration which comprises contacting at least one olefin capable of undergoing double bond isomerization with a catalyst system of (I) organoalkali metal compound and (II) potassium salt of a fatty acid or alcohol.

2. The process according to claim 1 wherein said olefin is a l-olefin or internal olefin containing 4 to 20 carbon 55 atoms per molecule.

3. The process according to claim 2 wherein said organoalkali metal compound can be represented by RM wherein M is lithium, sodium, potassium, rubidium, or cesium, R is a hydrocarbon radical of up to 20 carbon atoms per group, and x is an integer of 1 to 4;

5. The process according to claim 4 which employs a mole ratio of catalyst systemrolefin of about 10:1 to 01:1.

6. The process according to claim 5 wherein the process is conducted at temperatures of about 0 to C. in the presence of an inert atmosphere at pressures sufficient to maintain substantially liquid operations.

7. The process according to claim 6 further employing an inert diluent other than the olefin itself.

8. The process according to claim 6 wherein said olefin is butene-l, said organoalkali metal compound is n-butyllithium, said potassium compound is potassium tertpentyloxide.

9. The process according to claim 6 wherein said olefin is a mixture of trans/cis-butene-Z, and said organoalkali metal compound is n-butyllithium, said potassium compound is potassium tert-pentyloxide.

10. The process according to claim 6 wherein said olefin is pentene-l, and said organoalkali metal compound is n-butyllithium, said potassium compound is potassium tert-pentyloxide.

11. The process according to claim 6 wherein said olefin is pentene-Z, and said organoalkali metal compound is n-butyllithium, said potassium compound is potassium tert-pentyloxide.

References Cited UNITED STATES PATENTS 3,185,744 5/1965 Broaddus 260-6832 3,270,084 8/1966 Schriesheim et a1. 260683.2 3,309,410 3/1967 Schriesheim et a1. 260-666 3,542,896 11/1970 Butte 260683.2

OTHER REFERENCES Morton et al., J. Org. Chem, vol. 20, pp. 839-844, 1955.

DELBERT E. GANTZ, Primary Examiner C. E. SPRESSER, 1a., Assistant Examiner US. Cl. X.R. 260-666 A 

